Process for preventing caking and obtaining flowability of alkali chlorides and salt mixtures thereof

ABSTRACT

Caking of industrial alkali metal chlorides and mixtures containing them in storage is prevented and a flowable product is obtained by adding a hydrophilic and/or a hydrophobic material, in combination with a complex iron cyanide, on a hydroxyl group containing carrier to produce a permanent moisture content of at least 0.01 weight percent of water on the salt.

This is a division of application Ser. No. 579,158 filed May 20, 1975,and now U.S. Pat. No. 4,051,228.

The invention is directed to a process for the prevention of cakingtogether and for preserving the flowability of salts, specificallyalkali chlorides, e.g. sodium chloride or potassium chloride, and alkalichloride containing industrial salt mixtures during storage. Theinvention also encompasses the anticaking salt compositions thus formed.

Economization and automization of industrial processes in an increasingmeasure require that the materials used thereby do not cake together,flow freely and be easily dosable. However, it is known that manyinorganic salts in the form of finely divided crystallizates orgranulates harden after a relatively short time in storage or alsoduring transportation. This makes for considerable difficulty in thehandling of the product. Already in emptying the silo in the productionworks there is increased operation expense and danger points on accountof this tendency to harden designated generally as caking together. Thesalt must be disintegrated from the outside by a mechanical auxiliaryapparatus and be brought into motion in order to be emptied or loaded.In removing of the salt mountain with a dredger because of thehardening, there frequently remain standing steep walls which reach tothe peaks of the salt mountain and suddenly collapse and can fill up thedredger. Also in using the salt the dosing or mixing together with othersubstances is injured to a considerable extent by the caking together.Therefore there have not lacked attempts to find ways and means toreduce or entirely eliminate this tendency of salts to harden.

One of the best known processes consists of mixing in the dry form withsalts having a tendency to harden, finely divided fillers, as forexample silica, alkali, alkaline earth and aluminum silicates, aluminumoxide, magnesium oxide, calcium oxide or alkaline earth carbonate. Theseadditives form a loose jacket around the individual salt crystals orgranulates which in the recrystallization of the salt prevent aformation of bridges between the individual particles and therewith thecaking together. The disadvantages of these frequently water insolubleadditives are that they must be used in relatively large amounts inorder to produce a suitable effect. Through these high additives theproducts are inclined to be powdery and also lose most of their clearsolubility in water. Besides for mixing the additives with an anticakeresistent finished salt, there is required very effective mixingapparatuses which as a rule are very expensive.

Frequently the hydrophobizing action of organic substances such as oils,glycerines, paraffins, paraffin oils, alkyl sulfonates or fatty aminesis also sufficient for the anticaking finishing of salts. Theseadditives for the most part have the disadvantage that they can only beplaced on the salt with great industrial expense, for example as melts.A dosing of the hot salts, as it comes out of the production, by meansof coco-fatty amines is practically impossible because of the odortroubles and danger to health associated therewith. It must beundertaken in a separate working step before the loading of the coldsalt. In the interim storage of the salt therefore there is noprotection before the caking together.

Besides it has long been known that the hardening of alkali chloridescan be reduced by an addition of complex iron cyanides. These productsare also added in combination with agents for improving the freezingbehavior of the salt. If the alkali chlorides are contaminated withother materials, above all alkaline earth compound, frequently theanticaking finishing with complex iron cyanides fails to work. Alsoadditives which cause a precipitation or masking of the alkaline earthions, in many cases bring about no improvement of the anti-cakingproperties of the salts by addition of complex iron cyanides.

The invention is based on the problem of developing a process forpreventing the caking together in storage and obtaining a flowableindustrial alkali chloride, e.g. sodium chloride, potassium chloride oralkali chloride containing industrial salt mixture, which process in anindustrially simpler manner leads to an optimally flowable salt mixturewhile avoiding the above mentioned disadvantages.

This problem is solved according to the invention by adding ahydrophilic material and/or a hydrophobic material in combination with acomplex iron cyanide on a hydroxyl group containing carrier to produce apermanent moisture content of at least 0.01 weight percent H₂ O on thesalt.

This can be accomplished in the simplest manner by dosing the powderyanticaking agent with a metering trough to the salt stream flowing onthe conveyer belt at a suitable place between the drier and silo in asuitable amount. In the turning, standing or plowing through of the saltstream as well as in flowing into the silo there occurs sufficientmixing of the powdery anticaking agent with the salt. In this way therecan also be produced in large scale production units a good anticakingresult without especial industrial expense.

Each of the constituents of the anticaking agent of the invention hasits own special function. However only in the interplay of allcomponents is the desired anticaking effect produced. The caking of thesalt is known to depend upon the fact that on account of moistureabsorption and evolution under changing climate conditions on thesurface of the salt particles a recrystallization occurs in which thesalt particles cake together. If the recrystallization is prevented, thesalt also does not cake the salt together. According to the invention,by adding hydrophilizing and hydrophobizing materials the water contentof the salt is regulated in such a way that under changing climateconditions there is always a fixed residual moisture of at least 0.01weight percent H₂ O remaining on the salt. If a recrystallization of thesalt should occur under extreme conditions, the addition of the complexiron cyanide guarantees that the crystallizing salt forms no solidbridges but only loose dendritic compounds. For these three componentsto be effective it is necessary that they be distributed homogeneouslyon the surface of the salt particles by simple means and without greatindustrial expense. This is obtained by the invention by adding thematerials not directly but on a carrier. This carrier is a waterinsoluble highly dispersed compound which permits itself to be welldistributed in the salt and also remains held on the surface of the saltcrystals under extreme conditions of moisture. Because of its hydroxylgroups it likewise contributes to regulating the moisture content of thesalt. On the other hand it causes the complex iron cyanide to belocalized at exactly the place and to remain held where the danger ofgrowing together of the salt crystals is the greatest.

As hydrophilizing active components above all compounds of thepolycarboxylate type have been found advantageous. Examples of suchcompounds are polyacrylates poly(alpha hydroxyacrylates), homo andcopolymers of the maleic acid, e.g. styrene-maleic acid copolymer orother unsaturated di and polycarboxylic acid, for example itaconic acidor their corresponding salts, e.g. the sodium and potassium salts suchas sodium polyacrylate for example. It is especially advantageous to usesuch polycarboxylates which contain as functional groups besidespredominantly carboxyl or carboxylate groups additionally carboxyland/or hydroxyl groups. The average degree of polymerization of thepolycarboxylate, for short called POC, is between 5 and 500, preferablybetween 10 and 300, especially between 15 and 100. Processes for theproduction and building of the POC's are fully described in HaschkeGerman Offenlegungsschrift 1,904,941 Haschke U.S. Pat. No. 3,686,145 andcorresponding Haschke German Offenlegungsschrift 1,904,941, and HaschkeU.S. Pat. No. 3,793,222 and corresponding Haschke GermanOffenlegungsschrift 1,942,556. The entire disclosures of the two U.S.Haschke patents and Haschke German Offenlegungsschrift 1,904,940 arehereby incorporated by reference and relied upon. As further examples ofhydrophilizing active components there can also be used polyhydricalcohols such as glycerine or polyethylene glycols, e.g. tetraethyleneglycol or polyethylene glycol 400. In the process of the invention thehydrophilizing agent is used in an amount of 10 to 1000 ppm, preferably50-300 ppm based on the anticaking stable equipped salt.

A POC of Type A used in the composition of the invention ischaracterized by the following data; A poly-(aldehydrocarboxylic acid)solution is prepared by oxidative copolymerization of 20 mol percent ofacrylic acid with 80 mol percent of acrolein in aqueous 20 weightpercent hydrogen peroxide at 70° C (11.1 mol of acrolein per mol of H₂O₂ ; feeding the monomer mixture to the stirred hydrogen peroxide within4 hours). This solution was neutralized by adding 40 weight percentsodium hydroxide solution at 35° C after distillative separation of thegreatest part of the residual monomers and the neutralized mixturesubjected to the Cannizzaro reaction by further addition of NaOH up topH 12. After neutralization of the alkaline reaction mixture with aresidue of the above given poly(aldehydrocarboxylic acid) to pH 7 therewas obtained a 35 weight percent aqueous solution of apoly(hydroxycarboxylate) which is built of the following units of thegeneral formula and is described by the following parameters.

Y+ W/2 base mol percent units of the general formula: ##STR1##

U-W base mol percent units of the general formula: ##STR2##

Z base mol percent units of the general formula: ##STR3##

W/2 base mol percent units of the general formula: ##STR4##

V base mol percent units of the general formula: ##STR5##

A stands for an alkali metal, e.g. sodium or potassium, hydrogen or theammonium ion, R₁ stands for hydrogen, methyl, hydroxymethyl, ethyl,chlorine or bromine, preferably hydrogen or hydroxymethyl, R₂ and R₄ canbe the same or different and are hydrogen or hydroxymethyl, R₃ and R₅are likewise the same or different and are hydrogen, methyl or ethyl,preferably hydrogen, whereby as boundary conditions there must befulfilled that W is greater than 0.3 U as well as for such polymerswhich contain an appreciable number of units of general Formula IV, thequotient of the ground mol percent carboxyl or carboxylate groups andground mol percent of hydroxyl groups between 2 and 16, preferablybetween 2 and 9 especially between 3 and 8.

In POC, Type A, Y is 70 base mol percent, U is 17 base mol percent, V is13 base mol percent, W is 16 base mol percent and Z is 0 base molpercent. The average degree of polymerization (viscosity average) is P =20. From this data there is obtained an equivalent weight of the POCNasalt of 109.0 (with consideration of the degree of neutralization of0.88 as exists at a pH of 7 having regard to the analyticallydeterminable end groups).

The other POC, Type B, used in the composition of the invention ischaracterized by the following data.

A poly(aldehydocarboxylic acid) solution was produced by oxidativecopolymerization of 50 mol percent of acrylic acid with 50 mole percentof acrolein in aqueous 20 weight percent hydrogen peroxide at 70° C (1.1mol of acroleic per mol of H₂ O₂ feeding of the monomer mixture to thestirred hydrogen peroxide within 4 hours). This solution was neutralizedby adding 45 weight percent sodium hydroxide solution at 35° C afterdistillative separation of the greatest part of the residual monomersand the neutralized mixture subjected to the Cannizzaro reaction byfurther addition of NaOH up to pH 12. After neutralization of thealkaline reaction mixture with a residue of the above givenpoly(aldehydocarboxylic acid) to pH 7 there was obtained a 36 weightpercent aqueous solution of a poly (hydroxycarboxylates) which isdescribed by the following parameters.

Y is 78 base mol percent.

U is 16 base mol percent.

V is 6 base mol percent.

W is 15 base mol percent.

Z is 0 base mol percent.

The average degree of polymerization (viscosity average) is P = 60. Fromthis data there is obtained an equivalent weight of the POC Na salt of101.5 (with consideration of the degree of neutralization of 0.88 asexists at a pH of 7 having regard to the analytically determinable endgroups). The same formula units for the letters Y, U, V, W and Z arevalid as are described with Type A.

As hydrophobizing active components there can be used above allorganosilicon compounds, polywaxes*, paraffin waxes** and highersaturated fatty acids, e.g. of 12 to 18 carbon atoms as for examplestearic acid, lauric acid and palmitic acid and other long chain fattyacids. As organic silanes there may be especially mentionedpropyltrialkoxy silane, e.g. propyl trimethoxy silane, propyl triethoxysilane and propyltributoxy silane, polypropyl siloxane andmethylsiloxane. The oxides can also be hydrophobized in the manner shownin Laufer Patent No. 3,873,337 the entire disclosure of which is herebyincorporated by reference and relied upon. Based on the anticakingstable equipped salt there is used 10-1000 ppm, preferably 50-300 ppm.

As complex iron cyanides there can be employed all commercial hexacyanoferrates of alkali and alkaline earth metals. Especially approved aresodium ferrocyanide, potassium ferrocyanide and calcium ferrocyanide.The complex cyanide is used in an amount of 10-1000 ppm, preferably50-300 ppm based on the anticaking stable equipped salt.

As insoluble carriers there are especially suited inorganic finelydivided materials with a secondary particle size between 0.1 and 150μ,preferably 0.2 to 20μ, which have hydroxyl groups or are able to formhydroxyl groups in the production of the anticaking agents.

It is especially advantageous to employ finely divided precipitated orpyrogenically obtain metal oxides and/or metalloid oxides, especiallySiO₂ or Al₂ O₃ in the form of individual oxides, mixed oxides, oxidemixtures or mixtures of oxides.

These four types of oxides are described more specifically in thedrawings wherein:

FIG. 1 illustrates mixed oxides;

FIG. 2 illustrates oxide mixtures;

FIG. 3 illustrates mixtures of oxides, and

FIG. 4 illustrates individual oxides.

Referring more specifically to the drawings, FIG. 1 shows mixed oxidesof Al₂ O₃ in SiO₂. There is a building of foreign oxides into theprimary particles. There are flocks of a so-called mixed oxide, forexample Al₂ O₃ on SiO₂. By agitating the particles in water there areformed stable sols in aqueous dispersion. The mixed oxides can beprepared according to Wagner Canadian Pat. No. 573,556 and Wagner U.S.Pat. No. 2,951,044. The mixed oxides are produced from a mixture of twovolatile metal or metalloid halides using combustible gases and oxygenin a flame with water formation (hydrolytic decomposition). The twovolatile halides come out of a single burner nozzle with reaction in thenozzle to form the mixed oxides. One production process. The entiredisclosures of the Canadian and U.S. Wagner patents are herebyincorporated by reference and relied upon.

FIG. 2 shows oxide mixtures (or co-coagulates) of SiO₂ and Al₂ O₃. Thereare flocks of separate primary particles, so-called co-coagulates (oxidemixtures), for example SiO₂ /Al₂ O₃. The oxide mixture (orco-coagulates) can be prepared according to Wagner German Pat. No.1,066,552, Wagner U.S. Pat. No. 3,103,495 or Wagner U.S. Pat. No.2,951,044, Col. 3, lines 33 et seq. Two volatile metal compounds, forexample SiCl₄ and TiCl₄ were reacted from two nozzles in (one or) twoflames or flame chambers and jointly coagulated. Two volatile not mixedmaterials from two nozzles in a flame chamber. One production process.The entire disclosures of the Wagner German patent and both Wagner U.S.patents are hereby incorporated by reference and relied upon.

FIG. 3 shows mixtures of oxides specifically Al₂ O₃ and SiO₂. There areseveral separate flocks. However, each flock consists of primaryparticles. Examples are SiO₂ and Al₂ O₃ as thickening agents. Themixture of oxides can be produced according to Marsden U.S. Pat. No.2,965,568. Thus the oxide mixture can be formed by mechanical mixing oftwo or more oxides recovered in separate processes pyrogenically or byprecipitation or naturally. There are several methods of production andfrom these separate mixing processes. The entire disclosure of U.S. Pat.No. 2,965,568 is hereby incorporated by reference and relied upon.

FIG. 4 shows individual particles of an oxide specifically SiO₂. Theyare flocks of unitary primary particles (flocks = secondary particles),for example SiO₂ (Aerosil). The oxide is produced according to Bommer,German Auslegeschrift 1,150,955; Brunner German Auslegeschrift 1,163,784and Brunner German Auslegeschrift 1,210,421. The unitary oxide isproduced from a volatile metal or metalloid compound with combustiblegases and oxygen in a flame with water formation (hydrolyticdecomposition). The entire disclosures of the three GermanAuslegeschrifts are hereby incorporated by reference and relied upon.

There can be used not only inorganic oxides, but also other inorganiccompounds such as alkali and/or alkaline earth and/or alumino silicates,e.g. sodium silicate, potassium silicate, magnesium silicate, calciumsilicate, zeolite (a sodium aluminosilicate). These products have aspecific BET surface area of about 50-500 m² /g, preferably 180-230 m²/g. The silanol group density is between 1 and 10 SiOH/100 A²,preferably 3-6 SiOH/100 A². The adsorbed moisture of the product isbetween 0.5 and 10 weight percent preferably between 3 and 6 weightpercent. Carriers of this structure can absorb up to 40 weight percentof moisture without losing the appearance of a dry powder. In this formthey are able to hold the active components bound in a kind ofsolid-dispersion. In order to be able to absorb the active components inthis form the portion of the carrier material in the anticaking mixturemust be 30-70 weight percent, preferably 40-50 weight percent. Thiscorresponds to an additive amount of about 100-500 ppm, preferably200-300 ppm of carrier based on the anticaking stable equipped salt. Theamount of anticaking agent added, however, can be so regulated that itamounts to 50 to 1000 ppm, preferably 100 to 1000 ppm based on the salttreated.

According to the invention it is not only important that the activecomponents be added in suitable proportions in reference to the carrierand the equipped salt but to be added in the form of a speciallyproduced anticaking mixture. This mixture can be produced by dry mixingthe carrier in suitable proportions with the active materials in anintensive mixer and sufficient water added to this mixture that theactive components go into solution and as such are drawn into thecarrier material without this changing its character as a dry, freeflowing powder. The amount of water is preferably 30-50%, especially35-45% based on the total mixture of the anticaking agent. The mixing ofthe components suitable takes place at room temperature (i.e. about 20°C) or slightly elevated temperature. The pH value of the mixture isadjusted to y to 9, preferably 7 to 8.

Unless otherwise indicated all parts and percentages are by weight.

The following examples illustrate the process of the invention incomparison with the use of known anticaking agents.

There were carried out laboratory experiments as well as experiments onan industrial scale under the proper conditions in practice. As theanticaking equipped salts there were used several types of potassiumchloride, whose chlorine content was 47.2%, equal to 99.3% KCl; theimpurities included 0.2% Mg and 002% Ca. The pH value of the saturatedsolution was 10.5. The different types of potassium chloride differedmore or less only by the different particle sizes and particlestructure. The standard form of the salt contained about 17% fineportion below 400μ, while the coarse form of the salt was composed of24% salt particles between 400 and 630μ, 62% of particles between 630and 1000μ and 14% of particles >1000μ. Besides there was used a KClgranulate whose particle size was practically 100% >1000μ.

EXAMPLE 1

In a first series of experiments the coarse form of KCl was treated inan intensive mixer with the following anticaking agent solutions per kgof salt.

(1) 2 ml of a solution containing 10% Na₄ [Fe(CN)₆ ] . 10 H₂ O

(2) 10 ml of a solution containing 2% Na₄ [Fe(CN)₆ ] . 10 H₂ O + 5% Na₂CO₃

(3) 10 ml of a solution containing 2% Na₄ [Fe(CN)₆ ] . 10 H₂ O + 10% Na₂CO₃

(4) 10 ml of a solution containing 2% Na₄ [Fe(CN)₆ ] . 10 H₂ O + 20% Na₂CO₃

(5) 10 ml of a solution containing 2% Na₄ [Fe(CN)₆ ] . 10 H₂ O + 2.5%EDTA Na₄

(6) 10 ml of a solution containing 2% Na₄ [Fe(CN)₆ ] . 10 H₂ O + 10%EDTA Na₄

(7) 10 ml of a solution containing 2% Na₄ [Fe(CN)₆ ] . 10 H₂ O + 20%EDTA Na₄

(8) 10 ml of a solution containing 2% Na₄ [Fe(CN)₆ ] . 10 H₂ O + 5% NTANa₃

(9) 10 ml of a solution containing 2% Na₄ [Fe(CN)₆ ] . 10 H₂ O + 15% NTANa₃

(10) 10 ml of a solution containing 2% Na₄ [Fe(CN)₆ ] . 10 H₂ O + 2%POC, Type A

(11) 10 ml of a solution containing 2% Na₄ [Fe (CN)₆ ] . 10 H₂ O + 5%POC, Type A

(12) 10 ml of a solution containing 2% Na₄ [Fe(CN)₆ ] . 10 H₂ O + 15POC, Type A

(13) 2 ml of a solution containing 10% Ca₂ [Fe(CN)₆ ] . 11 H₂ O

(14) 2 ml of a solution containing 10% Ca₂ [Fe(CN)₆ ] . 11 H₂ O + 3%CaCl₂

EDTA Na₄ is the sodium salt of ethylenediamine tetraacetic acid and NTANa₃ is the sodium salt of nitrilotriacetic acid.

The samples were subsequently stored for several weeks in a changingclimate at above 80% relative humidity or below 30% relative humiditiesand normal temperature (i.e. about 20° C) and the anticaking activitymeasured by the depth of penetration of a test needle and also bymeasuring the resistance of crushing by a punch having a 1 kg/cm² load.The results of this series of tests are set forth in Table 1 and permitthe following summary:

While the non-dosaged samples after 8 weeks storage with 8 climatechanges had measured a resistance to crushing of 195 kg, the bestdosaged sample 2 hardened substantially less:

It had a resistance to crushing of only 27.3 kg. In a further foursamples (Nos. 3, 6, 10, and 13 with different anticaking agentcombinations the hardening of the salt could be lowered about 76-80%.

                                      TABLE 1                                     __________________________________________________________________________    EXAMPLE 1                                                                                                       Depth of penetration of test                Anticaking agent - addition in ppm                                                                              needle in cm after the                                                                             Crushing Resis-                                      POC test times           tance in kg            Sample                                                                            Na.sub.4 Fe(CN).sub.6 . 10H.sub.2 0                                                             EDTA                                                                              NTA Type                                                                              3 weeks                                                                            4 weeks                                                                             6 weeks                                                                            8 weeks                                                                            after 8 weeks          No. (Samples 1-12)                                                                             Na.sub.2 CO.sub.3                                                                  Na.sub.4                                                                          Na.sub.3                                                                          A   3 turns                                                                            3 turns                                                                             7 turns                                                                            7 turns                                                                            and 8                  __________________________________________________________________________                                                           turns                  1   200          --   --  --  --  0 - 1                                                                              >14   0    0    83.3                   2   200           500 --  --  --  >14  5 - 6 1 - 2                                                                              0    27.3                   3   200          1000 --  --  --  >14  6     1 - 4                                                                              0 - 1                                                                              45.2                   4   200          2000 --  --  --  0 - 1                                                                              --    --   --   --                     5   200          --    250                                                                              --  --  >14  4     3 - 4                                                                              0    77.7                   6   200          --   1000                                                                              --  --  1 - 2                                                                              1 - 2 1    0    44.7                   7   200          --   2000                                                                              --  --   11  1 - 4 1    0    55.7                   8   200          --   --   500                                                                              --  0 - 1                                                                              --    --   --   --                     9   200          --   --  1500                                                                              --  0 - 1                                                                              --    --   --   --                     10  200          --   --  --  200 0 - 1                                                                              7 - 9 0 - 1                                                                              0    46.2                   11  200          --   --  --  500 0 - 1                                                                              0 - 2 1    0    51.7                   12  200          --   --  --  1500                                                                              0 - 1                                                                              3 - 4 3    0    179                    13  200          --   --  --  --  11 - 14                                                                             9 - >14                                                                            5    0    41                         Ca.sub.2 Fe(CN).sub.6 . 11H.sub.2 O                                       14  . 200        --   --  --  --  11 - 14                                                                            >14   >14  1 - 2                                                                              174                        Ca.sub.2 Fe(CN).sub.6 . 11H.sub.2 +                                           60 CaCl.sub.2                                                             0   None         --   --  --  --  0 - 1                                                                              0 - 4 0    0    195                    __________________________________________________________________________

EXAMPLE 2

Based on the results of the preliminary tests (Example 1) there werecarried out large scale experiments in a salt works in which for each100 metric tons of potassium chloride there were dosed in the followinganticaking additives.

(a) 300 liters of an aqueous solution containing 20kg Na₄ Fe(CN)₆ . 10H₂O, 49kg Na₂ CO₃ and 1kg of POC Type A; this corresponds to a dosing ofthe salt with 200 ppm Na₄ Fe(CN)₆ . 10H₂ O, 490 ppm Na₂ CO₃ and 10ppmPOC Type A.

(b) 60 liters of an aqueous solution containing 20kg Ca₂ Fe(CN)₆ . 11H₂O; which corresponds to a dosing of the salt with 200 ppm of Ca₂ Fe(CN)₆. 11H₂ O.

(c) 60 liters of a solution containing 30% Ca₂ Fe(CN)₆ . 11H₂ O and 8%CaCl₂ ; which corresponds to a dosing of the salt with 180 ppm of Ca₂Fe(CN)₆ . 11H₂ O and 48 ppm CaCl₂.

The solutions were sprayed from a nozzle on the salt still wet from thecentrifuge while the salt was transported to the drying plant in chaincase conveyer about 40 cm wide and at a velocity of 40-60 metric tons ofKCl per hour. At delivery of the ferrocyanide solution this salt stillcontained about 2% water. After the drying at 160° C the product wasconveyed by way of a conveyer belt and a chute into a large storage halland poured into a mountain. At the time of flowing into the silo thesalt still had a temperature of above 70° C. and only cooled slowlyduring the storage.

For control and quality checking of the anticaking equipment of thesalt, samples were drawn off from the storage hall at intervals of about15 minutes and the ferrocyanide content checked by a Berlin bluereaction. The analyses showed that the ferrocyanide did not changeduring the drying process and a good distribution on the salt wasproduced.

After 3 months storage the salt mountain was cut into tangentially witha shovel dredger and half carried away. This showed that the salt duringthe long storage indeed was not caked solid, but still hung together sostrongly that steep walls of the salt mountain remained. Thus thisdosing of the salt only leads to a partial improvement of the anticakingcondition.

EXAMPLE 3

In a further series of experiments, the KCl-standard article was dosedin a rotating tube at 120° C with the anticaking agent combinationsgiven in Table 2. The addition of the materials in part took place inthe form of aqueous solutions, another part as solid mixtures orindividual components. These test conditions correspond to a dosing ofthe salt in practice if it is conveyed to the silo after the drying andclassifying with conveyer belts, screw conveyers and othertransportation apparatus.

                                      TABLE 2                                     __________________________________________________________________________    EXAMPLE 3                                                                                                       Depth of penetration of test                                                  needle in cm after the                                                                            Crushing Resis-                                           test times          tance in Kg             Sample                            2 weeks                                                                            3 weeks                                                                            4 weeks                                                                            5 weeks                                                                             after 5 weeks          No. Anticaking agent - addition in ppm                                                                          4 changes                                                                          6 changes                                                                          8 changes                                                                          10 changes                                                                          and 10                 __________________________________________________________________________                                                           changes                15  200 Ca.sub.2 Fe(CN).sub.6 . 11H.sub.2 O + 100 Glycerine                                                     0    0    0    0    >250                    27  50 Ca.sub.2 Fe(CN).sub.6 . 11H.sub.2 O + 250 polyethylene-Glycol              (mol.wt.400)                  1 - 3                                                                              1    0    0    ˜ 10              33  50 Na.sub.4 Fe(CN).sub.6 . 10H.sub.2 O + 250 polyethylene-Glycol                                            2 - 3                                                                              1 - 2                                                                              1    0    ˜ 9               44  500 K (wet precipitated silica)                                                                             0    0    0    0    >150                    45  250 K (wet precipitated silica)                                                                             0    0    0    0    ˜100              48  65 Na.sub.4 Fe(CN).sub.6 . 10H.sub.2 O + 250 K                                                              2 - 3                                                                              1 - 2                                                                              1    0    ˜ 8               52  65 Ca.sub.2 Fe(CN).sub.6 . 11H.sub.2 O + 20 CaCl.sub.2 + 250                                                1 - 2                                                                              1    0    0    ˜ 70              34  100 Ca.sub.2 Fe(CN).sub.6 . 11H.sub.2 O + 180 Na.sub.2 CO.sub.3 - 250         K                             1 - 2                                                                              1    1    0    ˜ 12              38  100 Na.sub.4 Fe(CN).sub.6 . 11H.sub.2 O + 180 Na.sub.2 CO.sub.3 - 50          K                             0    0    0    0    >150                    63  100 Na.sub.4 Fe(CN).sub.6 . 10H.sub.2 O + 50 Stearic                                                        0cid 0    0    0    ˜ 90              63  65 Na.sub.4 Fe(CN).sub.6 . 10H.sub.2 O + 250 K + 500 Stearic acid             (St.A.)                       2 - 3                                                                              3 - 4                                                                              2 - 4                                                                              2 - 4                                                                              < 1                     64  130 Na.sub.4 Fe(CN).sub.6 . 10H.sub.2 O + 500 K + 50                                                        5 - 7                                                                              3 - 4                                                                              2 - 4                                                                              3 - 4                                                                              < 1                     65  130 Na.sub.4 Fe(CN).sub.6 . 10H.sub. 2 O + 500 K + 10                                                       7 - 9                                                                              4    3 - 4                                                                              3 - 4                                                                              ˜ 1               66  65 Na.sub.4 Fe(CN).sub.6 . 10H.sub.2 O + 250 K + 50                                                         6 - 8                                                                              6    5 - 7                                                                              5 - 6                                                                              >> 1                    67  65 Na.sub.4 Fe(CN).sub.6 . 10H.sub.2 O + 250 K + 5 St.A.                                                    5 - 8                                                                              4    5 - 6                                                                              5    ˜ 1               73  100 Na.sub.4 Fe(CN).sub.6 . 10H.sub.2 O + 100 D(hydrophoric                                                 5 - 6a)                                                                            2 - 3                                                                              3    1 - 3                                                                              ˜ 3               71  100 Na.sub.4 Fe(CN).sub.6 . 10H.sub.2 O + 50 St.A. + 7.5                                                    5 - 7                                                                              4 - 6                                                                              3 - 5                                                                              4 - 5                                                                              ˜ 1               77  30 n-Propyltrimethoxysilane   5    2    3    2 - 4                                                                              ˜ 3               79  200 n-Propyltrimethoxysilane  5    0    1    1 - 2                                                                              ˜ 12              52  200 K.sub.4 Fe(CN).sub.6 . 3H.sub.2 O + 50 n-Propyltrimethoxysilane                                          10  3 - 4                                                                              1 - 3                                                                              1 - 3                                                                              ˜ 2               37  200 K.sub.4 Fe(CN).sub.6 . 3H.sub.2 O + 200 ES-Wax-Emuls.                                                   7    4    3 - 5                                                                              3 - 4                                                                              ˜ 9               90  200 Ca.sub.2 Fe(CN).sub.6 . 11H.sub.2 O + 200 ES-Wax-Emuls.                                                 6    3    3 - 4                                                                              2 - 3                                                                              ˜ 15              91  200 POC, Type B               7 - 9                                                                              8    7 - 8                                                                              6 - 8                                                                              < 1                     92  100 POC, Type B               7    7    7 - 9                                                                              7    < 1                     __________________________________________________________________________

For testing of the anticaking activity of the additives the samples wereagain stored in a changing claim at over 80% relative humidity or below30% relative humidity and normal temperature for several weeks and atseveral time intervals the penetration pressure of a test needle and thecrushing resistance measured with a punch having a 1kg/cm² load. Theresults of this series of tests are likewise collected in Table 2 andpermit the following interpretation.

The combination of ferrocyanides and hydrophilizing products such asglycerine or polyethylene glycol (Samples Nos. 15, 27 and 33) onlycauses a partial reduction of the degree of hardening of the salt. Thepolyethylene glycol used had a molecular weight of about 400. Theaddition of the substances took place in the form of an aqueous solutionin an amount of 2ml/kg of salt. After 5 weeks storage of the saltsamples and 10 climate changes the salt was so strongly clumped togetherthat the test needle loaded with 200 grams could not penetrate anycentimeter more into the salt.

In a further series of experiments a wet precipitated silica designatedas K (88% SiO₂, 0.3% Al₂ O₃, 0.5% SO₃, 0.6% Na₂ O, 6% adsorbed moisture,5.7 SiOH/100 A², BET surface area 230m² /g) in addition amounts of50-500 ppm was tested alone and in combination with other compounds. Thesamples 44 and 45 show that by adding only K there can be producedneither an improvement in the degree of hardening nor the desiredflowability of the salt. Also combinations with different ferrocyanides,calcium chloride and sodium carbonate brought about only certain gradualimprovements (Samples Nos. 48, 52, 34). However, if there aresimultaneously added a certain amount of stearic acid there is produceda clearly improved anticaking result (Sample Nos. 68, 63, 64, 65, 66,67). Also in combination with the hydrophobe silica D (92% SiO₂, 0.1%Al₂ O₃, 3% C in the form of methyl groups, 0.2% SO₃, 3% adsorbedmoisture, BET surface area 110m² /g, average primary particle size 18μm)the anticaking activity of the ferrocyanide is substantially increased(Sample Nos. 73, 71).

Hydrophobizing agents such as n-propyltrimethoxysilane, which are addedin aqueous alcoholic solutions effect either alone or in combinationwith ferrocyanide only a gradual improvement (Sample Nos. 77, 79, 82).Comparable results are obtained if in place of then-propyltrimethoxysilane there is added an aqueous emulsion of ES-wax incombination with ferrocyanides (Sample Nos. 87, 90).

A very good anticaking action was produced in this series of experimentsalso with POC, Type B, when it was added in the form of an aqueoussolution (10ml/kg of salt) in amounts of 100 or 200 ppm based on the hotsalt.

EXAMPLE 4

In a further large scale experiment in the salt works the followinganticaking agents were added for dosing in each case 100 metric tons ofpotassium chloride.

(a) A solution of 120 grams/l of Na₄ Fe(CN)₆.10H₂ O + 120 grams/l of Na₂CO₃ + 2.5 grams/l of POC, Type B. Each time there were added 1.7 litersof this solution per ton of potassium chloride. This corresponds to adosing with about 200 ppm sodium ferrocyanide, 200 ppm Na₂ CO₃ and 4 ppmPOC Type B.

(b) A solution of 29.1% Ca₂ Fe(CN)₆.11H₂ O + 8% CaCl₂. The amount ofsolution added was 0.8 liter per ton of KCl and corresponds to a dosingwith about 230 ppm Ca₂ Fe(CN)₆.11H₂ O and 85 ppm CaCl₂.

(c) A solid mixture consisting of 41% K (wet precipitated silica), 10%Na₄ Fe(CN)₆.10H₂ O, 8% stearic acid and 41% water. There was added about600 grams of this mixture per ton of KCl. This corresponds to a dosingwith about 250 ppm K, 65 ppm sodium ferrocyanide and 50 ppm stearicacid.

(d) A 20% solution of POC, Type B. This solution was added in amounts of1 liter per ton of KCl; this corresponds to a dosing with about 200 ppmPOC, Type B.

The anticaking agents were added in this experiment to the dry but stillat about 120° C hot salt while it ran from a chute onto a conveyer belt.A pumping apparatus with an automatic performance indicator and a unarynozzle which permitted a homogenous spraying of the salt stream wereinserted for dosing the solution. The solid mixture was added by adosing trough to the potassium chloride.

The salt dosed with the various anticaking agents were subsequentlyconveyed into a silo and stored in four separate salt mountains. Duringthe charging into the silo at time intervals of about 10 minutes sampleswere drawn and it was established through analysis that a gooddistribution of the anticaking agent could be produced also in thismanner. After about 3 months of storage the anticaking behavior of thefour salt mountains was again tested by tangentially cutting into thesalt mountain with a tractor shovel.

After the interval the best results were produced with anticakingmixture (c). The salt mountain was only coated with an easily crushablecovering layer. In the experiment, in order to climb the mountain onesank knee deep into the salt. Because of the continuously dropping saltit was not possible to come to the peak of the mountain. In thetangential removing of the tapered salt mountain the salt droppedimmediately and again formed a shallow angle of repose. This resultcorresponds to the ideas of the salt industry.

An equally good result was produced with anticaking agent (d). This saltmountain was also coated only with a thin cover layer, which, however,was somewhat stronger than in the experiment with mixture (c) andpermitted the salt mountain to be walked through with trouble. Inremoving of the mountain the salt likewise dropped. However, it built asteeper sloping angle than with sample (c).

The salt mountains closed with anticaking mixtures (a) and (b) were lesswell cut away. The salt mountains were both coated by a harder coveringlayer which also held together somewhat more strongly so that in theremoving of the mountain relatively steep walls remained. In comparisonto the non dosed salt there was established to be sure, a certainimprovement in the degree of hardening, however the effect wasinsufficient.

EXAMPLE 5

In a further large scale experiment in the salt works the productionmixture of KCl standard article and coarse articles were dosed with thefollowing anticaking additives in powder form.

(a) 65 ppm K₄ Fe(CN)₆.3H₂ O, 250 ppm K (wet precipitated silica), 50 ppmof staric acid, 0.1 ppm milori blue and 250 ppm water.

(b) 65 ppm K₄ Fe(CN)₆.3H₂ O, 250 ppm K, 50 ppm POC Type B, 0.1 ppmmilori blue and 250 ppm water.

(c) 65 ppm Na₄ Fe(CN)₆.10H₂ O, 250 ppm K, 25 ppm POC (Type B), 25 ppmstearic acid and 250 ppm water.

The addition of the anticaking additives took place in the form ofhomogeneous anticaking agent mixtures which produced the followingresults.

Mixture (a): There were mixed for 5 minutes in an intensive mixer with ausable volume of 150 liters 25.0 kg of K (wet precipitated silica), 6.5kg of K₄ Fe(CN)₆.3H₂ O in powder form, 10 grams of Milori blue and 5.0kg of powdery stearic acid and then inside another 5 minutes there wereadded 25 liters of water and mixing continued for a further 10 minutes.There were obtained thereby 61.5 kg of a powdery readily flowableanticaking agent with a bulk density (apparent density) of about 600grams/l, which is storage stable and not clumped together.

Mixture (b): There were present in an intensive mixer with a usablevolume of 150 liters 25.0 kg of K and there were added to the runningmixer within 5 minutes a solution of 6.5 kg of K₄ Fe(CN)₆.3H₂ O, 10grams of Milori blue and 5.0 kg of POC (Type B) in 25 liters ofwater.The mixing was continued for a further 10 minutes and the powdery,easily dosable anticaking agent discharged.

Mixture (c): There were present in an intensive mixer with a usablevolume of 150 liters 25.0 kg of K and 2.5 kg of powdery stearic acid andthere were added to the running mixer in 5 portions within 5 minutes asolution of 6.5 kg of Na₄ Fe(CN)₆.10H₂ O and 2.5 kg. of POC Type B in 25liters of water. Then thorough mixing was containued for 10 minutes andthe powdery, readily flowable anticaking agent discharged.

The dosing of the anticaking agent again took place using a dosingtrough on the dry, hot salt. After addition of the anticaking agent thesalt was also mixed on the conveyer belt by a plowshare system. Tocompensate for the yellow tinge of the salt there were simultaneouslydropped on the wet salt pump before the drying tube, a calciumferrocyanide solution. The amount added was about 10 ppm of Ca₂Fe(CN)₆.11H₂ O.

Separate 100 ton lots of potassium chloride were dosed with each of thethree anticaking agents just mentioned and stored separately in thesilo. After 4 weeks of storage the salt mountain was tested forflowability by culling in with a tractor shovel. In all three mountainssubsequently slid homogeneously and always formed again a smooth debriscone. In this experiment there also could not be established a formationof a crust on the surface of the salt mountain, although the climaticconditions changed drastically during the storage time and periods withvery high air humidity were produced. In the half excavated of a fourthsalt mountain without additive on the contrary there remained steepwalls. The salt dosed with the anticaking agents differed from the nondosed salt at the same time by a white appearance. This result suits thedesires of the salt industry.

The composition can comprise, consist essentially of or consist of thestated materials and the process can comprise, consist essentially of orconsist of the steps set forth.

What is claimed is:
 1. A flowable alkali metal chloride compositionresistant to caking on storage including as an anticaking agent (A) acomplex iron cyanide (B) a water insoluble, inorganic, inert, finelydivided hydroxyl group containing precipitated or pyrogenically formedmetal oxide or metalloid oxide carrier material, (C) a hydrophobizingmaterial and (D) a polycarboxylate hydrophilizing material, saidmaterials (A), (C) and (D) being present on B, said anticaking agentproviding a permanent moisture content of at least 0.01 weight % ofwater on the salt.
 2. A flowable composition according to claim 1wherein (A) is an alkali hexacyanoferrate or alkaline earth metalhexacyanoferrate and (C) is stearic acid.
 3. A flowable compositionaccording to claim 2 wherein (A) is sodium, potassium or calciumferrocyanide.
 4. A composition according to claim 2 wherein (B) is Al₂O₃ or SiO₂ or a mixture of at least two of these oxides in the form ofindividual oxides, mixed oxides, oxide mixtures or mechanical mixturesof these oxides.
 5. A composition according to claim 2 wherein (B) is awet precipitated silica having a secondary particle size of 0.2 to 20μm,a specific surface area between 180 and 230 m² /g an adsorbed moisturein the range of 3 to 6 weight % and a silanol group density between 3 to6 SiOH/100 A and is present in an amount of 0.01 to 0.1, a weight basedon the alkali metal chloride.
 6. A flowable composition according toclaim 1 wherein (A) is an alkali hexacyanoferrate or alkaline earthmetal hexacyanoferrate.
 7. A flowable composition according to claim 6wherein (A) is sodium, potassium or calcium ferrocyanide.
 8. A flowablecomposition according to claim 7 wherein the alkali metal chloride issodium chloride or potassium chloride.
 9. A process of preparing theproduct of claim 7 comprising adding (A) to (C) and (D) on the hydroxylgroup containing (B) carrier to the alkali metal chloride.
 10. Acomposition according to claim 6 wherein (B) is Al₂ O₃ or SiO₂ or amixture of at least two of these oxides in the form of individualoxides, mixed oxides, oxide mixture or mechanical mixtures of theseoxides.
 11. A composition according to claim 6 wherein (B) is a wetprecipitated silica having a secondary particle size of 0.2 to 20μm, aspecific surface area between 180 and 230 m² /g an adsorbed moisture inthe range of 3 to 6 weight % and a silanol group density between 3 to 6SiOH/100 A and is present in an amount of 0.01 to 0.1 weight % based onthe alkali metal chloride.
 12. A composition according to claim 9 where(C) is stearic acid and is present in an amount of 0.001 to 0.1 weight %based on the alkali metal chloride.
 13. A composition according to claim12 wherein (C) is present in an amount of 0.005 to 0.02 weight % basedon the alkali metal chloride.
 14. A composition according to claim 6where (D) is a polycarboxylate and is present in an amount of 0.001 to0.1 weight % based on the alkali metal chloride.